Ethylene-vinyl alcohol copolymers (hereinafter, may be abbreviated as EVOH) are excellent in transparency, a gas barrier property, flavor retention, solvent resistance, oil resistance, and the like, and making good use of such properties, are used for wide use including various packaging containers, such as food packaging containers, medical product packaging containers, industrial chemical packaging containers, and agrochemical packaging containers.
For production of such molded article, EVOH is often melt molded, and after that, is secondary processed. For example, stretching in an effort to improve mechanical strength and thermoforming of a multilayer sheet including an EVOH layer to make a container shape are widely carried out.
In recent years, there are increasing demands for stretching at a higher draw ratio and obtaining a molded article in a deeper drawing shape by thermoforming. Since EVOH is a resin having a high modulus of elasticity, there are also increasing demands for a resin having greater flexibility. From such a situation, a resin is desired that is improved in secondary processability and flexibility without decreasing performances, such as transparency, a gas barrier property, flavor retention, solvent resistance, and oil resistance, that EVOH originally has as much as possible.
Patent Document 1 describes modified EVOH obtained by reacting a monofunctional epoxy compound with a hydroxyl group of EVOH and describes that flexibility and secondary processability of the EVOH are improved. However, since the modified EVOH is obtained by reacting an epoxy compound with EVOH in a molten state, there have been problems of increasing production steps and rising production costs.
Patent Document 2 describes a packaging material which has a layer of a composition having a plurality of endothermic peaks in a melting curve by DSC measurement, made by blending a plurality of EVOHs having different vinyl alcohol contents, and describes that it is excellent in a gas barrier property, mechanical properties, and processability. However, in this case, it has not been easy to manage both the gas barrier property and the secondary processability at a high level and it has also been unavoidable to decrease the transparency.
Patent Document 3 describes modified EVOH that is obtained by copolymerizing ethylene, vinyl acetate, and 3,4-diacetoxy-1-butene and then saponifying it, and in which 3,4-dihydroxy-1-butene units are copolymerized, and describes that the modified EVOH is excellent in stretchability, a gas barrier property, appearance, and strength. However, since 3,4-diacetoxy-1-butene has the polymerization reactivity that is equivalent compared with vinyl acetate, most of it turns out to remain after polymerization when the copolymer is taken out at a low conversion. Therefore, loads of washing and wastewater treatment have increased and a rise in production costs have also been unavoidable.
In general, EVOH is often used as a multilayer structure with another thermoplastic resin, such as polyolefin, polystyrene, polyester, and polyamide. However, these thermoplastic resins and EVOH have poor adhesion and are laminated via an adhesive resin, such as maleic anhydride modified polyolefin (polyethylene, polypropylene, ethylene-vinyl acetate copolymer) and an ethylene-ethyl acrylate-maleic anhydride copolymer, but still there are cases that delamination occurs. Accordingly, a resin is also desired that is improved in interlayer adhesion without decreasing performances, such as transparency, a gas barrier property, flavor retention, solvent resistance, and oil resistance, that EVOH originally has as much as possible.
Patent Document 4 describes a coinjection stretch blow molded container of a thermoplastic polyester layer and an EVOH composition layer. The EVOH composition has two kinds of EVOH with different degrees of saponification blended therein, and thus, it is described that good interlayer adhesion is obtained. However, since EVOH having a low degree of saponification is used, there have been cases that thermal stability during melt molding decreases and long-run moldability becomes insufficient.
Patent Document 5 describes that an adhesive layer containing a thermoplastic resin that contains a boronic acid group or a functional group capable of being converted into a boronic acid group in the presence of water is used for production of a multilayer structure including an EVOH layer and another thermoplastic resin layer, and it is described that the multilayer structure thus obtained is excellent in interlayer adhesion. However, since the thermoplastic resin that contains a boronic acid group or a functional group capable of being converted into a boronic acid group in the presence of water is expensive, it has been desired to use an adhesive resin that is more inexpensive and is for general purpose.
Patent Document 6 describes an EVOH composition that contains 500 to 2000 ppm of alkali metal salt in terms of metal elements, and it is described that a multilayer structure including a layer of the EVOH composition has good interlayer adhesion. However, since the EVOH composition contains a large amount of alkali metal salt, the thermal stability at high temperatures is insufficient. For example, for production of a film using the EVOH composition, there has been a risk that problems of defects in appearance, such as coloration, fish eyes, and longitudinal streaks, and odor due to a decomposition gas occur.
Heat shrink films are widely used as a packaging material for foods and the like. In particular, heat shrink films are preferably used as a packaging material for foods that are non-uniform in shape and size, such as meat and its processed foods. Packaging materials for foods are desired to be excellent in a gas barrier property for freshness preservation of the food and excellent in flavor retention. From such a situation, heat shrink films are desired to be, in addition to being excellent in thermal shrinkage, excellent in a gas barrier property, flavor retention, and the like.
As a barrier material used for heat shrink films, polyvinylidene chloride is known (Patent Document 7). However, a toxic gas is generated when a film using polyvinylidene chloride is incinerated. Accordingly, loads on the environment have been great.
In recent years, heat shrink films that are stretched at a higher ratio are desired. By stretching at a high ratio, thermal shrinkage percentage is improved. From such a situation, heat shrink films are desired that are improved in stretchability and thermal shrinkage without decreasing performances, such as transparency, a gas barrier property, flavor retention, solvent resistance, and oil resistance, that EVOH originally has as much as possible.
Patent Document 1 describes a heat shrink film using modified EVOH that is obtained by reacting a monofunctional epoxy compound with a hydroxyl group of EVOH. An example in Patent Document 1 describes a heat shrink film having a layer of the modified EVOH, and it is described that the heat shrink film was good in stretchability, a gas barrier property, and thermal shrinkage. However, as described above, there has been a problem with the modified EVOH that production costs rise. Further, there have been cases that the heat shrink film is insufficient in a barrier property, stretchability, thermal shrinkage, and the like.
Patent Document 3 describes a heat shrink film using modified EVOH that is obtained by copolymerizing ethylene, vinyl acetate, and 3,4-diacetoxy-1-butene and then saponifying it, and in which 3,4-dihydroxy-1-butene units are copolymerized. Then, it is described that the heat shrink film was excellent in stretchability, thermal shrinkage, a gas barrier property, transparency, and delamination resistance. However, as described above, there have been problems with the modified EVOH described in Patent Document 3 that loads of washing and wastewater treatment increase after polymerization and production costs rise. Further, there have been cases that the heat shrink film is still insufficient in a barrier property, stretchability, thermal shrinkage, and the like.
Stretch blow molded containers are used as containers for foods and the like. For example, thermoplastic polyester (hereinafter, may be abbreviated as PES) containers by stretch blow molding are excellent in a variety of properties, such as transparency, mechanical properties, and flavor retention, and moreover, have little concern of elution of residual monomers and harmful additives when employed to be a molded article and are excellent in hygiene and safety, so that they are used in a wide range of fields. However, since their gas barrier properties are not always sufficient, it has been difficult to store beverages, foods, and the like for a long period.
Meanwhile, a coinjection stretch blow molded container using an EVOH layer as a barrier layer is reported. The coinjection stretch blow molded container is produced by, after forming a parison (container precursor), stretch blow molding the parison thus obtained. Generally, a method of producing a parison includes coinjection molding, coextrusion molding, multi-stage injection molding, and the like. Among them, coinjection molding is characterized in that the apparatus is simple, that it generates few scraps such as trimmings and the like, and further that it is possible to structure an EVOH layer completely covered with a PES layer and the like and thus a multilayer containers of good appearance is obtained due to the contact effect by the atmospheric pressure even without an adhesive resin layer between the EVOH layer and the PES layer.
However, when containers filled with beverages, foods, and the like are shocked, for example, by dropping them, separation (delamination) easily occurs between a PES layer and an EVOH layer, which has been a serious problem.
From such a situation, a barrier resin is desired that is excellent in adhesion to another resin and is also flexible. In addition, there are also increasing demands for improvement in moldability. From such a situation, a resin is desired that is improved in adhesion, flexibility, and moldability without decreasing performances, such as transparency, a gas barrier property, flavor retention, solvent resistance, and oil resistance, that EVOH originally has as much as possible.
Patent Document 1 describes a coinjection stretch blow molded container prepared using modified EVOH that is obtained by reacting a monofunctional epoxy compound with a hydroxyl group of EVOH. Then, it is described that the container was capable of preventing interlayer delamination due to impact and was excellent in transparency and a barrier property. However, as described above, there has been a problem with the modified EVOH that production costs rise.
Patent Document 3 describes a coinjection stretch blow molded container prepared using modified EVOH that is obtained by copolymerizing ethylene, vinyl acetate, and 3,4-diacetoxy-1-butene and then saponifying it, and in which 3,4-dihydroxy-1-butene units are copolymerized. Then, it is described that the container was excellent in impact delamination resistance, transparency, pressure resistance, and pressure resistance uniformity. However, as described above, there have been problems with the modified EVOH described in Patent Document 3 that loads of washing and wastewater treatment increase after polymerization and production costs rise.
As a plastic fuel container, those of a monolayer type made of polyethylene are used but they have a disadvantage of having relatively high gasoline permeability. In contrast, a multilayer fuel container is proposed that uses nylon for a barrier layer, that is equipped with high density polyethylene layers on its both sides via adhesive resin layers, and that has a three-material five-layer structure. In addition, a fuel container is also proposed in which nylon is dispersed in a discontinuous thin layer form in a polyethylene layer by mixing nylon with polyethylene for melt extrusion.
However, these fuel containers have been still insufficient in a gasoline barrier property. In addition, they have had a problem in barrier properties to gasoline (hereinafter, may be abbreviated as oxygenated gasoline) in which an oxygen element containing compound, such as methanol, ethanol, and methyl tertiary butyl ether (MTBE), is blended with gasoline, biodiesel fuel that contains biologically derived fatty acid ester, and the like.
Meanwhile, EVOH is also excellent in a fuel barrier property. Then, containers having an EVOH layer are known that they have a fuel barrier property better than the fuel containers described above. However, EVOH has a high modulus of elasticity and there have been cases that the impact resistance becomes a problem in a large container, a container in a complex shape, and the like. Since EVOH has low adhesion to another resin, multilayer containers obtained by laminating EVOH and another resin also have had a problem that delamination due to impact easily occurs. In addition, since EVOH has a high modulus of elasticity, it used not to be easy to secondarily process in a deep drawing shape or in a complex shape.
From such a situation, a resin is desired that is excellent in flexibility and adhesion to another thermoplastic resin and also excellent in secondary processability. That is, a resin is desired that is improved in flexibility, adhesion, and secondary processability without decreasing a fuel barrier property that EVOH originally has as much as possible.
Patent Document 8 describes a fuel container having a layer modified EVOH that is obtained by reacting a monofunctional epoxy compound with a hydroxyl group of EVOH. Then, it is described that the fuel container was good in a fuel barrier property, impact resistance, and moldability. However, as described above, there has been a problem with the modified EVOH that production costs rise.
Patent Document 3 describes a fuel container having a layer of modified EVOH that is obtained by copolymerizing ethylene, vinyl acetate, and 3,4-diacetoxy-1-butene and then saponifying it, and in which 3,4-dihydroxy-1-butene units are copolymerized and it is described that the fuel container is excellent in a fuel barrier performance and the like. However, as described above, there have been problems with the modified EVOH described in Patent Document 3 that loads of washing and wastewater treatment increase after polymerization and production costs rise.